For the purpose of a maintenance service, in a plant, operation data having an amount of several tens of thousands of points is gathered per second for every site. If operation data measured in the plant is all gathered and kept in a storage of a server as it is, data having an amount of several gigabytes is accumulated in the storage everyday.
Thus, in 2 to 3 months, a storage having a capacity of about a terabyte inevitably becomes full of data stored therein. Accordingly, there is raised a problem that, even though it is naturally desirable to provide a storage capable of accumulating data generated in several years for the purpose of a maintenance service, data gathered previously in several preceding months must be erased.
On the other hand, operation data measured by sensors installed at several hundreds of positions on a heavy machine and large-size equipment is gathered at a high speed in a short period of typically 50 milliseconds. In this case, data gathered on a day for each piece of equipment attains an amount of the order of gigabytes.
In order to render an advanced state base maintenance service in the future, it is necessary to increase the number of measurement points per site or per piece of equipment and the measurement frequency from their respective present values. In addition, it is also necessary to raise the number of sites handled by a server computer for rendering the maintenance service as well as the number of equipment pieces for the computer. It is possible to imagine that, in the near future, the amount of data kept in a server computer will be equal to a value of the order of terabytes per day and, in few years, the amount of such data will increase to a value of the order of petabytes.
Thus, instead of keeping the gathered operation data as it is, the gathered operation data is compressed or portions of the data are deleted so that it is possible to reduce the load borne in keeping the data or to decrease the amount of stored data.
In order to implement what is described above, there is provided an irreversible compression method (or a thinning method) in accordance with which, an allowable data error is set in advance and only data having errors bigger than the allowable data error is kept and stored while the remaining data is discarded.
As examples of the compression method, there have been proposed dead-band compression or change-rate compression like ones disclosed in Non-patent Document 1, swing-door compression like one disclosed in Non-patent Document 2 and compression making use of a virtual straight line like one described in Patent Document 2.
In addition, in order to adopt the above-stated compressions more effectively, there has been provided a compression method described in Patent Document 1. In accordance with this compression method, a data compression rate (or an allowable error) is not fixed at an initial set value determined at the time of designing a system. Instead, the data compression rate (or the allowable error) is changed dynamically in accordance with an abnormality (or an alarm) generated by a plant or equipment and an event such as an operation so that, at a normal time, high compression is carried out and, in the event of an abnormality, the compression rate is reduced or no compression is carried out. In this way, it is possible to prevent data required for the maintenance service from being lost and reduce the amount of stored data.
In order to render a good state base maintenance service, on the other hand, there has been provided an equipment-abnormality predicting and diagnosing technology. For example, Patent Document 3 describes an abnormality predicting and diagnosing technology adopting vector quantization clustering. For information on a vector quantization technology, refer to Non-patent Document 3. For information on clustering (or a cluster analysis), on the other hand, refer to Non-patent Document 4.